Likely derieved from 其 (that; those (he; she; it; they)) which in turn seems to have been derieved from Proto-Austroasiatic *kɨ (third person pronoun).

The reason why I think it derieves from 其 instead of directly from PAA is that "kia" doesn't have the "third person pronoun" sense.

@范俊華: Do you have a source? If no, you should probably discuss atWiktionary:Etymology scriptorium first.RcAlex36 (talk)16:05, 24 September 2020 (UTC)Reply

Personally, I wouldn't argue with this. Vietnamese hasđó andđấy, which are both clearly native, while the n-series of demonstratives has so many similar form throughout Asia that it's troublesome to deal with.PhanAnh123 (talk)16:07, 24 September 2020 (UTC)Reply

There's problem with the diphthong, though (and cases likebìa probably isn't going to help solve it).PhanAnh123 (talk)16:25, 24 September 2020 (UTC)Reply